The present invention relates to a process for distillatively separating a mixture containing a vinyl ether of the general formula (I)R1—O—CH═CH2   (I)and alcohol of the general formula (II)R2—OH   (II)in which R1 and R2 are each independently a saturated or unsaturated, aliphatic or cycloaliphatic radical having from 2 to 10 carbon atoms, and in which the alcohol (II) has a boiling point which is at least 1° C. higher, measured at or extrapolated to 0.1 MPa abs, than the vinyl ether (I).
Vinyl ethers constitute an important compound class having a wide field of use. For instance, they find use, inter alia, as monomer building blocks in polymers and copolymers, in coatings, adhesives, printing inks and in radiation-curative coating materials. Further fields of use are the preparation of intermediates, fragrances and flavors, and also pharmaceutical products.
Vinyl ethers are generally prepared industrially by reacting the appropriate alcohols with ethyne in the presence of basic catalysts (see Ullmann's Encyclopedia of Industrial Chemistry, 6th edition, 2000 Electronic Release, Chapter “VINYL ETHERS—Production” and W. Reppe et al., Justus Liebigs Ann. Chem., 601 (1956), pages 135 to 138). In addition to the catalyst and possible by-products, the reaction mixture formed comprises mainly the vinyl ether formed and the unconverted alcohol. The two latter components, apart from the C1 derivatives, methyl vinyl ether/methanol, cannot be separated by simple distillation into fractions of the desired purity as a consequence of azeotrope formation. This problem has hitherto been solved by the use of extraction and extraction distillation processes, in which one or more extraneous substances are added as auxiliaries and then removed again after separation into a vinyl ether- and an alcohol-containing fraction.
For instance, EP-A 0 415 334 describes the one- or multistage extraction of a vinyl ether- and alcohol-containing mixture with an aqueous solution of a base, in which a vinyl ether phse and an aqueous alcoholic phase are obtained and the alcohol is then obtained by distillation from the aqueous alcoholic phase.
U.S. Pat. No. 2,779,720 describes a process for separating a mixture which comprises an aliphatic vinyl ether and an aliphatic alcohol, in which this mixture is distilled together with water and a glycol or glycol ether. The top product formed in this case is an azeotropic mixture of the vinyl ether and water, from which the vinyl ether can be obtained in a further distillation. The bottom product remaining is a mixture comprising the alcohol and glycol or glycol ether, from which the alcohol can be obtained by a downstream distillation.
DE-A 1 000 804 discloses a process for working up a mixture which comprises a monovinyl ether of a polyhydric alcohol and a polyhydric alcohol, in which this mixture is distilled together with water in an alkaline medium or subjected to a steam distillation. The top product obtained in this case is an azeotropic mixture of the vinyl ether with water, and the residue remaining in the bottom is the alcohol. The top fraction obtained in the distillation may optionally be extracted with a water-immiscible solvent to transfer the vinyl ether to the organic phase, from which it can be obtained by distillation.
SU 1 616 888 describes the separation of a butanol- and butyl vinyl ether-containing mixture by extractive distillation with water. The azeotropic mixture formed as a top product which contains the butyl vinyl ether and water is subsequently distilled to obtain the butyl vinyl ether. The butanol-containing bottom product of the first distillation is worked up in a further distillation to obtain butanol.
U.S. Pat. No. 3,878,058 describes a process for obtaining alkyl vinyl ethers from a mixture containing the alkyl vinyl ether and an aliphatic alcohol, in which this mixture is distilled together with a glycol monoether. In this process, the top product removed is the alkyl vinyl ether and the bottom product obtained is an alcohol- and glycol monoether-containing mixture. This is separated in a subsequent distillation into the alcohol and the glycol monoether, and the latter is recycled to the first distillation stage.
A disadvantage of all of the abovementioned processes is the use of one or more extraneous substances as auxiliaries. This adds new compounds to the system which subsequently have to be removed again. This is associated firstly with corresponding cost and inconvenience relating to the apparatus and process, and secondly with the risk of contamination of the vinyl ether and/or of the alcohol by residual amounts of these extraneous substances. In addition, as a consequence of their intrinsic volume, the extraneous substances reduce the capacity of the distillation apparatus or require the use of larger distillation apparatus.